1. Field of the Invention
The present invention relates to a ceramic honeycomb structural body used for a catalyst carrier for purifying an exhaust gas of an internal combustion engine, a filter for trapping soot, or a catalyst carrier for purifying and/or deodorizing a firing gas of fuels such as petroleum, various kinds of gases and the like.
2. Description of the Related Art
Usually, as for a catalyst carrier for purifying an exhaust gas of an internal combustion engine, a filter for trapping soot, or a catalyst carrier for purifying and/or deodorizing a firing gas of fuels such as petroleum, various kinds of gases and the like, use is made of a ceramic honeycomb structural body made of cordierite, mullite and the like.
FIG. 5 is a cross sectional view showing one embodiment of a known ceramic honeycomb structural body 13. As shown in FIG. 5A, the ceramic honeycomb structural body 13 comprises an outer wall 16 and a plurality of cells 12 formed by through holes extending in a gas flow direction, which are defined by partition walls 11 arranged in the outer wall 16. In the known ceramic honeycomb structural body 13, all the cells 12 including a complete cell 12a and an incomplete cell 12b extend through from one end of the ceramic honeycomb structural body 13 to the other end. In this case, the complete cell 12a means a cell having a complete square cross section, and it is arranged in a center portion of the ceramic honeycomb structural body 13. Moreover, the incomplete cell 12b means a cell not having a complete square cross section, and it is arranged in an outermost peripheral portion of the ceramic honeycomb structural body 13.
In order to eliminate a crack generation at the outermost peripheral portion of the known ceramic honeycomb structural body 13 shown in FIG. 5A, Japanese Patent Publication No. 63-12658 (JP-B-63-12658) discloses a ceramic honeycomb structural body 15, in which all the cells 12c arranged near the outermost peripheral portion are sealed by ceramic materials 14 having a heat resistivity as shown in FIG. 5B. In this case, the ceramic materials 14 are arranged into the cells 12 along a 10 mm distance from the end of the ceramic honeycomb structural body 15.
In the known ceramic honeycomb structural body 13 having the constitution shown in FIG. 5A, if the outer wall 16 and the partition walls 11 of the ceramic honeycomb structural body 13 are thin, they are liable to be transformed as shown in FIG. 6A, or the outer wall 16 is not formed continuously and a gap 17 is generated in the outer wall 16 as shown in FIG. 6B. In these cases, an endurable applied pressure strength of the ceramic honeycomb structural body 13 is weakened. Therefore, a crack is generated in the ceramic honeycomb structural body 13, and, in an extreme case, the ceramic honeycomb structural body 13 is broken when assembled as a catalyst converter. Moreover, if being assembled as a catalyst converter, an exhaust gas does not pass through the cell 12, but passes through a metal wire portion which supports the ceramic honeycomb structural body 13 via a breakage portion due to the transformation of the partition walls 11 or through the gap 17. Therefore, it is not possible to achieve a sufficient purifying operation.
Moreover, in the incomplete cell 12b of the known ceramic honeycomb structural body 13, a catalyst 18 to be carried is thicker in excess as shown in FIG. 6C, and thus the catalyst 18 is wasted. Therefore, if the ceramic honeycomb structural body 13 is assembled in a catalyst converter 19 by supporting only its side surface as shown in FIG. 7, it is not possible to use the catalyst effectively, since an exhaust gas does not easy to flow due to a stuffing or a half-stuffing of the incomplete cell 12b.
Further, in the known ceramic honeycomb structural body 15 having the constitution shown in FIG. 5B, a plurality of the cells 12 are sealed by the ceramic materials 14 at the outer peripheral portion. In this case, if the sealing is performed at both ends of the ceramic honeycomb structural body 15, the catalyst to be carried is not wasted. However, since an exhaust gas does not flow in these sealed cells 12, a volume of the ceramic honeycomb structural body 15 is increased correspondingly. Moreover, if the sealing is performed not at the both ends but at a center of the ceramic honeycomb structural body 15, the catalyst is wasted, since the catalyst is adhered in the cells 12 whose center is sealed. Therefore, these known ceramic honeycomb structural bodies are not convenient for a real use.